Prior research has determined that low-income students lose more ground over the summer than their higher-income peers. Prior research has also shown that some summer learning programs can stem this loss, but we do not know whether large, district-run, voluntary programs can improve students' outcomes. To fill this gap, The Wallace Foundation launched the National Summer Learning Study in 2011. This five-year study offers the first-ever assessment of the effectiveness of large-scale, voluntary, district-run, summer learning programs serving low-income elementary students. The study, conducted by RAND, uses a randomized controlled trial to assess the effects of district-run voluntary summer programs on student achievement and social and emotional skills over the short and long run. All students in the study were in the third grade as of spring 2013 and enrolled in a public school in one of five urban districts: Boston; Dallas; Duval County, Florida; Pittsburgh; or Rochester, New York. This report, the second of five that will result from the study, looks at how summer programs affected student performance on mathematics, reading, and social and emotional assessments in fall 2013. (author abstract)